Conventionally, a process of manufacturing a semiconductor device formed from a micropattern such as an LSI or VLSI adopts a reduction projection exposure apparatus which reduces a pattern formed on a reticle (mask) and projects and transfers it onto a substrate coated with a photosensitive agent. To increase the degree of integration of a semiconductor element, further micropatterning is required. The exposure apparatus takes a measure to attain micropatterning along with the development of a resist process.
As a technique for increasing the resolving power of an exposure apparatus, a method of shortening the exposure wavelength or a method of increasing the numerical aperture (NA) of a projection optical system is used. In general, the resolving power is known to be proportional to the exposure wavelength and inversely proportional to the NA.
As such a measure for micropatterning is taken, the throughput of an exposure apparatus is further improved in view of the manufacturing cost of semiconductor elements. For example, there is available a method of shortening the exposure time per shot by increasing the output from an exposure light source, or a method of increasing the number of elements per shot by widening an exposure area.
However, vibration conducted to an exposure apparatus for micropattern exposure from its installation floor, or slight vibration or deformation generated by a built-in movable unit (for example, a mask stage or substrate stage) degrades the overlay exposure accuracy or exposure image accuracy. Furthermore, if exposure is not executed until such vibration or deformation is reduced, the throughput decreases.
A conventional exposure apparatus adopts a technique for supporting its main body portion by an anti-vibration table or a technique for absorbing a reaction force in acceleration/deceleration of the built-in movable unit, in order to reduce the influence of floor vibration or its internal vibration.
As described above, however, the NA of a projection optical system and an exposure area are getting larger, and the output from a light source increases. Moreover, the use of a modified illumination method which controls the distribution of a secondary source with various manners and illuminates to attain high resolution is spreading. As a result, the size and weight of an illumination optical system are increasing. This may have an influence on a vibration suppression characteristic with respect to the apparatus main body.
To solve this problem, a method of arranging a light source or illumination optical system separately from the exposure apparatus main body portion is known to be effective.
Japanese Patent Laid-Open No. 2003-158059 discloses an exposure apparatus which supports an illumination optical system separately from its main body portion. This apparatus uses a sensor to measure the relative position between the illumination optical system and the main body portion, and means which calibrates the sensor. Japanese Patent Laid-Open No. 2003-158059 also discloses the following techniques. When an abnormality is found on the basis of a measurement value obtained by the sensor, a light source, reticle driving means, and substrate driving means are stopped. When an actuator corrects the orientation of the illumination optical system to be a normal state, the exposure operation is restarted. However, Japanese Patent Laid-Open No. 2003-158059 does not disclose any technique for dynamically controlling the orientation of the illumination optical system so as to correct, during exposure, the relative position between the illumination optical system and the main body portion on the basis of the output from the sensor.
As micronization of the pattern to be transferred onto a substrate advances, the positional relationship between the illumination optical system and the main body portion need be held in the original state more strictly. For example, assume that the relative positional relationship between the main body portion and the illumination optical system varies upon a change in orientation of the main body portion. At this time, an optical axis deviation or incident angle deviation of illumination light occurs. This makes illuminance nonuniform or deforms the exposure image, so required exposure accuracy cannot be satisfied. Furthermore, the wait time until vibration is attenuated increases, resulting in a decrease in throughput.